1. Field of the Invention
The present invention relates generally to liquid crystal display and more specifically to a method and a system for fabricating LCD panels by with a reduced angular misalignment between the anisotropic axes of laminated layers.
2. Description of the Related Art
Liquid crystal displays, such as twisted nematic type, usually comprise a liquid crystal layer and a pair of orientation (alignment) layers, one on each side of the liquid crystal layer, to cause their molecules to twist along its thickness and orient in mutually orthogonal directions on its opposite surface when no voltage is applied. On the outer side of each orientation layer is a polarization film so arranged that its polarization (anisotropic) is aligned with that of the orientation layer. When one of the polarization films is illuminated with natural light, only that portion of the incident light linearly aligned with the polarizaton axis of the film is allowed to enter the liquid crystal layer. Under zero electrical field, the linearly polarized light is subjected to a full 90-degree twist as it traverses the liquid crystal layer and allowed to pass through other polarization film, producing a maximum level of brightness (white luminance representation). When a full voltage is applied across the liquid crystal layer, the molecules are transposed in the direction of thickness, causing the polarized light aligned with one polarization film to be twisted out of alignment with the other polarization film, producing a maximum level of darkness (black luminance representation). In the IPS (in plane switching) type of liquid crystal displays, the axes of the orientation layers are equally aligned so that ON/OFF switching modes are in reverse to those of the twisted nematic types.
One of the important characteristics used to evaluate the quality of an LCD panel is the black-to-white contrast ratio, i.e., the ratio of the white luminance to the black luminance. Angular misalignment between the polarization film and the orientation layer, which may occur when they are pasted together, represents a potential cause of low contrast ratios. Experiments indicate that the angular misalignment of as small as 4 degrees causes the contrast ratio of LCD panels to decrease from the maximum value of 400 to as low as 150.
Mechanical methods are currently employed to align polarization films with the orientation layers of liquid crystal panels. However, due to manufacturing tolerances, precision alignment cannot consistently be obtained. As a result, variability exists in contrast ratio, which ranges significantly between 400 and 200 for misalignments of plus/minus 2 to 3 degrees.
To overcome this problem, Japanese Patent Publication 11-271778 discloses a method in which a polarization film is initially pasted on one surface of a liquid crystal layer where a light sensitive layer is applied and ultraviolet light of 350 nanometers is then used to illuminate the liquid crystal layer through the polarization film. The molecules in the illuminated light sensitive layer are excited and their axis is oriented in the same direction as the polarization film.
However, suitable materials for use with such orientation layers are not available at present.
In addition, optical compensation films are currently used in LCD panels. The films of this type is a birefringence characteristic that compensates for the loss of light transmissivity of the panel when viewed at a skewed angle. Since this optical compensation film has an anisotropic axis, it must be aligned with the axis of a polarization film when they are pasted together.
It is therefore an object of the present invention to provide a method and system for fabricating a liquid crystal display that eliminates angular misalignment between optically anisotropic films and orientation layers.
According to a first aspect, the present invention provides a method of fabricating a liquid crystal display, comprising the steps of setting a liquid crystal display panel on a fixed base, the panel including a liquid crystal layer and an orientation layer on one surface of the liquid crystal layer, setting an anisotropic film relative to the orientation layer, directing linearly polarized light to the panel and the anisotropic film and detecting light therefrom, and adjusting angle of orientation of the anisotropic film relative to the orientation layer according to intensity of the detected light.
According to a second aspect, the present invention provides a method of fabricating a liquid crystal display, comprising the steps of setting a liquid crystal display panel on a fixed base, the panel including a liquid crystal layer and an orientation layer on one surface of the liquid crystal layer, setting an optical compensation film and a polarizer relative to the orientation layer, directing linearly polarized light to the panel, the optical compensation film and the polarizer at a skewed angle and detecting light therefrom, the linearly polarized light having a polarization axis aligned with polarization axis of the polarizer, and adjusting angle of orientation of the optical compensation film relative to the orientation layer according to intensity of the detected light.
According to a third aspect, the present invention provides a system for fabricating a liquid crystal display, comprising base means for setting a liquid crystal display panel, the panel including a liquid crystal layer and an orientation layer on one surface of the liquid crystal layer, carrier means for setting an anisotropic film relative to the orientation layer, a light source for directing linearly polarized light to the panel and the anisotropic film, and an optical sensor for detecting the directed light from the anisotropic film. The carrier means is rotatable so that angle of orientation of the anisotropic film can be adjusted relative to the orientation layer according to intensity of the detected light.
According to a fourth aspect, the present invention provides a system for fabricating a liquid crystal display, comprising base means for setting a liquid crystal display panel, the panel including a liquid crystal layer and an orientation layer on one surface of the liquid crystal layer, carrier means for setting an optical compensation film and a polarizer relative to the orientation layer, a light source for directing linearly polarized light to the panel, the optical compensation film and the polarizer at a skewed angle, and an optical sensor for detecting the directed light from the polarizer. The linearly polarized light has a polarization axis aligned with polarization axis of the polarizer. The carrier means is rotatable so that angle of orientation of the optical compensation film can be adjusted relative to the orientation layer according to intensity of the detected light.